An immersion freezer which employs a postcooling chamber containing a series of cascading conveyor belts is taught in the art. Specifically, Koach Engineering & Mfg. Inc. teaches such a freezer referred to as the "Nitrogen Immersion-Vapor Freezing System" (hereinafter the "Koach freezer") in a technical brochure entitled"Innovation and Efficiency in Food Freezing Equipment". (The Koach freezer, minus the cascading conveyor belt feature, is also taught in U.S. Pat. No. 4,403,479 by Rasovich.)
The immersion section of such a freezer initially immerses all or part of the items to be frozen (typically food items) in a bath of a liquid refrigerant to impart a crust freeze on the items, which locks in moisture and prevents clumping. The postcooling chamber then uses the vaporized refrigerant from the immersion section to complete the freezing process while also maximizing efficiency. The postcooling chamber also imparts agitation to the items (which further prevents clumping) through the use of a series of cascading conveyor belts.
There is a concern with the Koach freezer, however, in that the location of the postcooling chamber relative to the immersion section is not optimal. In the Koach freezer, the postcooling chamber is located adjacent to the immersion section. Contrast this with the present invention's freezer where the post cooling chamber is located underneath the immersion section. This design difference imparts three distinct advantages to the present invention's freezer as follows:
(1) The "footprint" of the present invention's freezer will be smaller and thus the present invention's freezer will require less factory floorspace. PA0 (2) Since both the immersion section and post cooling chamber are generally in the shape of elongated tunnels, by "stacking" the tunnels instead of having them adjacent to each other, not only is the footprint of the resulting freezer smaller but so is the exposed surface area. Since the heat leak of a freezer is proportional to the exposed surface area, this translates into less heat leak and hence better efficiency. PA0 (3) Both the Koach freezer and the present invention's freezer exploit the fact that it is space efficient to multipass the items as they move through the postcooling chamber. The number of multipasses however quickly reaches a point of diminishing return after one two passes tie starting at one end of the postcooling chamber, moving to the opposite end to create a first "level" of cascading belts and finally returning to the starting end to create a second "level" of cascading belts) from the standpoint of heat transfer to the product and therefore efficiency. This is because it is difficult for the vaporized refrigerant from the immersion section to penetrate beyond the second level of cascading belts in the postcooling chamber. Because the Koach freezer's postcooling chamber is adjacent to the immersion section, the cascading conveyor belts in Koach's postcooling chamber are forced to multipass three times in order to have the items finish up at the exit end of the freezer. This mandates a third, largely wasted level (in terms of heat transfer) in the Koach postcooling chamber that the present invention's bottom chamber design avoids.